A polymer electrolyte fuel cell using a proton-conductive solid polymer membrane operates at a low temperature, as compared with other types of fuel cells such as a solid oxide fuel cell and a molten carbonate fuel cell. Therefore, the polymer electrolyte fuel cell is expected to be used for a stationary power supply or a power source for a mobile unit such as an automobile, and has started to be practically used.
In the polymer electrolyte fuel cell as described above, an expensive metal catalyst as represented by Pt (platinum) and Pt alloy is generally used, and causes increased cost of the fuel cell. Therefore, the development of the technology that can reduce cost of a fuel cell by reducing the use amount of a noble metal catalyst has been required.
For example, JP 2007-250274 A (corresponding to US 2009/047559 A1) discloses an electrode catalyst having catalytic metal particles carried on a conductive carrier wherein an average particle size of the catalytic metal particles is larger than an average pore size of micropores in the conductive carrier. JP 2007-250274 A (corresponding to US 2009/047559 A1) describes that this configuration can prevent the catalytic metal particles from entering the micropores in the carrier to increase a ratio of catalytic metal particles used in three-phase boundary and to improve the utilization efficiency of an expensive noble metal.